Biphasic Anaphylaxis

 

Biphasic anaphylaxis is an anaphylactic episode followed by an asymptomatic period with the return of anaphylactic symptoms in the absence of further exposure to the triggering antigen. The incidence of secondary reaction following primary anaphylactic reaction can range from 1% to 23% and occurs in up to 23% of adults and up to 11% of children. The time interval from primary to secondary reaction ranges from 1 to 72 hours, though predominantly occurs within 8 hours of the primary event.

 

Anaphylaxis

Anaphylaxis is a sudden, severe allergic reaction that may cause death. The single most effective treatment for an episode of anaphylaxis is administration of epinephrine. Epinephrine is a chemical that arrests the chain of reactions that causes the signs and symptoms of anaphylaxis.

 

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Anaphylaxis

The mainstay of treatment is adrenaline (1:1000 concentration, given IM) at the doses below and can be repeated every 5 minutes:

  • Adult                                       = 500 micrograms IM (0.5mls)
  • Child more than 12 years    = 500 micrograms IM (0.5mls)
  • Child 6-12 years                   = 300 micrograms IM (0.3mls)
  • Child less than 6 years         = 150 micrograms IM (0.15mls)

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The Penicillin Allergy Myth Busted

Although a myth persists that approximately 10% of patients with a history of penicillin allergy will have an allergic reaction if given a cephalosporin, the overall cross-reactivity rate is approximately 1% when using first-generation cephalosporins or cephalosporins with similar R1 side chains.